1. Field of the Invention
The present invention relates to a liquid transport apparatus for transporting a liquid and a method for producing the same.
2. Description of the Related Art
A variety of liquid transport apparatuses capable of transporting liquids have been hitherto known. In particular, an ink-jet head is known, in which the ink is transported to nozzles to discharge the ink from the nozzles to the printing paper or the like. The ink-jet head includes a flow passage unit which is provided with a plurality of ink flow passages including pressure chambers communicated with nozzles, and an actuator unit which applies the pressure to the ink contained in the pressure chambers. The ink-jet head is constructed such that the pressure is selectively applied to the ink contained in the plurality of pressure chambers, and thus the ink is discharged from the nozzles communicated with the pressure chambers.
In the case of the ink-jet head as described above, when the ink flow passage is contaminated with bubbles coming from the outside, and the bubbles remain in the ink flow passage, then it is impossible to reliably apply the pressure to the ink contained in the pressure chamber (in the ink flow passage) by using the actuator unit. Therefore, the ink-jet head is generally constructed so that the purge operation can be executed to forcibly discharge the bubbles together with the ink from the nozzle. However, even when the purge operation is performed, it is difficult to discharge the bubbles adhered to the portion disposed in the vicinity of the wall surface of the ink flow passage, because the flow velocity of the ink is low in the vicinity of the wall surface. Therefore, in order to completely discharge the bubbles contained in the ink flow passage, it is necessary to repeatedly execute the purge operation many times. As a result, the ink is consumed uselessly in many cases. In view of the above, an ink-jet head has been suggested, which is constructed to enhance the flow velocity of the ink in the vicinity of the wall surface so that the bubbles can be discharged more reliably by generating a vortex flow in the ink flow passage.
For example, an ink-jet head described in Japanese Patent Application Laid-open No. 5-162311 is constructed such that an ink supply passage, which supplies the ink to a pressure chamber, is arranged on a tangential line of a side wall of the pressure chamber, and a vortex flow is generated in the pressure chamber when the ink inflows into the pressure chamber. On the other hand, an ink-jet head described in Japanese Patent Application Laid-open No. 1-297252 is constructed such that a spiral hole is formed in a filter provided at a halfway portion of an ink flow passage, and a vortex flow is generated in the ink flow passage by the aid of the hole.
In the case of the ink-jet head described in Japanese Patent Application Laid-open No. 5-162311, the bubbles, which remain in the pressure chamber, tend to be discharged with ease, because the vortex flow is formed in the pressure chamber. However, in reality, the ink flow passage, which is formed in the flow passage unit, includes many bent portions and many portions in which the flow passage area is increased/decreased, for example, at circumferential portions of the nozzle at which the flow passage area is suddenly decreased. The bubbles tend to remain especially easily at the corners which are formed at the portions as described above. However, it is difficult to completely discharge the bubbles remaining at the halfway portions of the ink flow passage as described above by only the vortex flow generated in the pressure chamber. On the other hand, in the case of the ink-jet head described in Japanese Patent Application Laid-open No. 1-297252, the bubbles, which partially remain around the filter, can be discharged owing to the action of the vortex flow generated by the spiral hole formed for the filter. However, in order to completely discharge the bubbles remaining in the ink flow passage, it is necessary that the filters each having the spiral hole should be provided at several portions of the ink flow passage. The flow passage resistance is increased as well, and this arrangement is also disadvantageous in view of the production cost.
In order to produce the ink flow passage of the ink-jet head, it is advantageous for the production to form the ink flow passage by stacking a plurality of plates. In such a procedure, ink flow holes, which reach the nozzle, are communicated with each other by forming the ink flow holes through the respective plates and stacking the plates. However, when the flow passage is formed by stacking the plates as described above, any stepped portion (or any corner portion) is formed between the adjoining plates in some cases. Bubbles tend to stay with ease at the stepped portion as described above. Even when the holes of the respective plates are designed to be identical in order to form the smooth flow passage, the hole positions are sometimes deviated by several micrometers to several tens micrometers between the adjoining plates when the plates are stacked. The positional deviation as described above causes the stepped portion between the adjoining plates. Therefore, the problem of the remaining bubbles is especially serious in the case of the ink-jet head of the type in which the flow passage is formed by stacking the plates (stacked type head).